Misplaced Pages

#443556

32-430: As of 2016, four incremental versions of a classification system have resulted from this collaboration, published in 1998, 2003, 2009 and 2016. An important motivation for the group was what they considered deficiencies in prior angiosperm classifications since they were not based on monophyletic groups (i.e., groups that include all the descendants of a common ancestor). APG publications are increasingly influential, with

64-405: A clade, but the dicots were not, with a number of former dicots being placed in separate groups basal to both monocots and the remaining dicots, the eudicots or 'true dicots'. The overall scheme was relatively simple. This consisted of a grade consisting of isolated taxa (referred to as ANITA ), followed by the major angiosperm radiation , clades of monocots, magnolids and eudicots. The last being

96-467: A common ancestor). An ordinal classification of flowering plant families was proposed as a "reference tool of broad utility". The broad approach adopted to defining the limits of orders resulted in the recognition of 40 orders, compared to, for example, 232 in Takhtajan's 1997 classification . In 1998 only a handful of families had been adequately studied, but the primary aim was to obtain a consensus on

128-473: A distinct group. At first there was a reluctance to develop a new system based entirely on a single gene. However, subsequent work continued to support these findings. These research studies involved an unprecedented collaboration between a very large number of scientists. Therefore, rather than naming all the individual contributors a decision was made to adopt the name Angiosperm Phylogeny Group classification, or APG for short. The first publication under this name

160-572: A grouping of taxa which meets these criteria: Monophyly is contrasted with paraphyly and polyphyly as shown in the second diagram. A paraphyletic grouping meets 1. but not 2., thus consisting of the descendants of a common ancestor, excepting one or more monophyletic subgroups. A polyphyletic grouping meets neither criterion, and instead serves to characterize convergent relationships of biological features rather than genetic relationships – for example, night-active primates, fruit trees, or aquatic insects. As such, these characteristic features of

192-400: A large clade with smaller subclades and two main groupings, rosids and asterids , each in turn having two major subclades. As the overall relationship between groups of flowering plants became clearer, the focus shifted to the family level, in particular those families generally accepted as problematic. Again, consensus was achieved relatively easily resulting in an updated classification at

224-489: A number of major herbaria changing the arrangement of their collections to match the latest APG system. In the past, classification systems were typically produced by an individual botanist or by a small group. The result was a large number of systems (see List of systems of plant taxonomy ). Different systems and their updates were generally favoured in different countries. Examples are the Engler system in continental Europe,

256-461: A polyphyletic grouping are not inherited from a common ancestor, but evolved independently. Monophyletic groups are typically characterised by shared derived characteristics ( synapomorphies ), which distinguish organisms in the clade from other organisms. An equivalent term is holophyly . The word "mono-phyly" means "one-tribe" in Greek. These definitions have taken some time to be accepted. When

288-548: Is a useful source for the latest research in angiosperm phylogeny which follows the APG approach. Other sources include the Angiosperm Phylogeny Poster and The Flowering Plants Handbook. a = listed as an author; c = listed as a contributor Monophyletic In biological cladistics for the classification of organisms , monophyly is the condition of a taxonomic grouping being a clade – that is,

320-459: Is significantly reduced. This requires the recognition of both new orders and new families compared to the previous classification. The number of orders goes up from 45 to 59; only 10 families are not placed in an order and only two of these ( Apodanthaceae and Cynomoriaceae ) are left entirely outside the classification. The authors say that they have tried to leave long-recognized families unchanged, while merging families with few genera. They "hope

352-642: The Bentham & Hooker system in Britain (particularly influential because it was used by Kew ), the Takhtajan system in the former Soviet Union and countries within its sphere of influence and the Cronquist system in the United States. Before the availability of genetic evidence, the classification of angiosperms (also known as flowering plants , Angiospermae , Anthophyta or Magnoliophyta )

SECTION 10

#1732773007444

384-409: The APG below). A classification presents a view at a particular point in time, based on a particular state of research. Independent researchers, including members of the APG, continue to publish their own views on areas of angiosperm taxonomy. Classifications change, however inconvenient this is to users. However, the APG publications are increasingly regarded as an authoritative point of reference and

416-525: The Asparagaceae or as separate families. Some of the main changes in APG II were: In 2007, a paper was published giving a linear ordering of the families in APG II, suitable for ordering herbarium specimens, for example. The third paper from the APG updates the system described in the 2003 paper. The broad outline of the system remains unchanged, but the number of previously unplaced families and genera

448-425: The basis of genetic characteristics. The paper explained the authors' view that there is a need for a classification system for angiosperms at the level of families, orders and above, but that existing classifications were "outdated". The main reason why existing systems were rejected was because they were not phylogenetic , i.e. not based on strictly monophyletic groups (groups which consist of all descendants of

480-417: The broader asparagus family ( Asparagaceae ). The authors say that alternative circumscriptions, as in APG I and II, are likely to cause confusion and that major herbaria which are re-arranging their collections in accordance with the APG approach have all agreed to use the more inclusive families. This approach is being increasingly used in collections in herbaria and botanic gardens . In the same volume of

512-404: The cladistics school of thought became mainstream in the 1960s, several alternative definitions were in use. Indeed, taxonomists sometimes used terms without defining them, leading to confusion in the early literature, a confusion which persists. The first diagram shows a phylogenetic tree with two monophyletic groups. The several groups and subgroups are particularly situated as branches of

544-458: The classification [...] will not need much further change." A major change is that the paper discontinues the use of 'bracketed' families in favour of larger, more inclusive families. As a result, the APG III system contains only 415 families, rather than the 457 of APG II. For example, the agave family ( Agavaceae ) and the hyacinth family ( Hyacinthaceae ) are no longer regarded as distinct from

576-545: The development of a fourth version there was some controversy over the methodology, and the development of a consensus proved more difficult than in previous iterations. In particular Peter Stevens questioned the validity of discussions regarding family delimitation in the absence of changes of phylogenetic relationships. Further progress was made by the use of large banks of genes, including those of plastid , mitochondrial and nuclear ribosomal origin, such as that of Douglas Soltis and colleagues (2011). The fourth version

608-413: The fact that a monophyletic group includes organisms (e.g., genera, species) consisting of all the descendants of a unique common ancestor. Conversely, the term polyphyly , or polyphyletic , builds on the ancient Greek prefix πολύς ( polús ), meaning "many, a lot of", and refers to the fact that a polyphyletic group includes organisms arising from multiple ancestral sources. By comparison,

640-467: The family level. The second paper published by the APG in 2003 presented an update to the original classification of 1998. The authors stated that changes were proposed only when there was "substantial new evidence" which supported them. The classification continued the tradition of seeking broad circumscriptions of taxa, for example trying to place small families containing only one genus in a larger group. The authors stated that they have generally accepted

672-408: The family name Asphodelaceae is used instead of Xanthorrhoeaceae , and Francoaceae is used instead of Melianthaceae (and now also includes Vivianiaceae ). This brings the total number of orders and families recognized in the APG system to 64 and 416, respectively. Two additional informal major clades, superrosids and superasterids , that each comprise the additional orders that are included in

SECTION 20

#1732773007444

704-462: The following are some examples of the influence of the APG system: The principles of the APG's approach to classification were set out in the first paper of 1998, and have remained unchanged in subsequent revisions. Briefly, these are: For a detailed discussion on phylogenetic nomenclature, see Cantino et al. (2007).) The initial 1998 paper by the APG made angiosperms the first large group of organisms to be systematically re-classified primarily on

736-418: The journal, two related papers were published. One gives a linear ordering of the families in APG III; as with the linear ordering published for APG II, this is intended for ordering herbarium specimens, for example. The other paper gives, for the first time, a classification of the families in APG III which uses formal taxonomic ranks ; previously only informal clade names were used above the ordinal level. In

768-638: The larger clades dominated by the rosids and asterids are also included. APG IV also uses the linear approach (LAPG) as advocated by Haston et al. (2009) In a supplemental file Byng et al. provide an alphabetical list of families by orders. Peter Stevens , one of the authors of all four of the APG papers, maintains a web site, the Angiosperm Phylogeny Website (APWeb), hosted by the Missouri Botanical Garden , which has been regularly updated since 2001, and

800-457: The naming of higher orders. Such a consensus proved relatively easy to achieve but the resultant tree was highly unresolved. That is, while the relationship of orders was established, their composition was not. Other features of the proposed classification included: A major outcome of the classification was the disappearance of the traditional division of the flowering plants into two groups, monocots and dicots . The monocots were recognized as

832-610: The term paraphyly , or paraphyletic , uses the ancient Greek prefix παρά ( pará ), meaning "beside, near", and refers to the situation in which one or several monophyletic subgroups are left apart from all other descendants of a unique common ancestor. That is, a paraphyletic group is nearly monophyletic, hence the prefix pará . On the broadest scale, definitions fall into two groups. The concepts of monophyly, paraphyly , and polyphyly have been used in deducing key genes for barcoding of diverse group of species. Takhtajan system A system of plant taxonomy ,

864-493: The tree to indicate ordered lineal relationships between all the organisms shown. Further, any group may (or may not) be considered a taxon by modern systematics , depending upon the selection of its members in relation to their common ancestor(s); see second and third diagrams. The term monophyly , or monophyletic , derives from the two Ancient Greek words μόνος ( mónos ), meaning "alone, only, unique", and φῦλον ( phûlon ), meaning "genus, species", and refers to

896-420: The views of specialists, although noting that specialists "nearly always favour splitting of groups" regarded as too varied in their morphology. APG II continued and indeed extends the use of alternative 'bracketed' taxa allowing the choice of either a large family or a number of smaller ones. For example, the large family Asparagaceae includes seven 'bracketed' families which can either be considered as part of

928-401: Was "rudely shattered". This posed problems for all users of classification systems (including encyclopaedists). The impetus came from a major molecular study published in 1993 based on 5000 flowering plants and a photosynthesis gene ( rbcL ). This produced a number of surprising results in terms of the relationships between groupings of plants, for instance the dicotyledons were not supported as

960-454: Was based on their morphology (particularly of their flower) and biochemistry (the kinds of chemical compounds in the plant). After the 1980s, detailed genetic evidence analysed by phylogenetic methods became available and while confirming or clarifying some relationships in existing classification systems, it radically changed others. This genetic evidence created a rapid increase in knowledge that led to many proposed changes; stability

992-916: Was finally published in 2016. It arose from an international conference hosted at the Royal Botanical Gardens in September 2015 and also an online survey of botanists and other users. The broad outline of the system remains unchanged but several new orders are included ( Boraginales , Dilleniales , Icacinales , Metteniusales and Vahliales ), some new families are recognised ( Kewaceae , Macarthuriaceae , Maundiaceae , Mazaceae , Microteaceae , Nyssaceae , Peraceae , Petenaeaceae and Petiveriaceae ) and some previously recognised families are lumped ( Aristolochiaceae now includes Lactoridaceae and Hydnoraceae ; Restionaceae now re-includes Anarthriaceae and Centrolepidaceae ; and Buxaceae now includes Haptanthaceae ). Due to nomenclatural issues,

Angiosperm Phylogeny Group - Misplaced Pages Continue

1024-436: Was in 1998, and attracted considerable media attention. The intention was to provide a widely accepted and more stable point of reference for angiosperm classification. As of 2016, three revisions have been published, in 2003 (APG II), in 2009 (APG III) and in 2016 (APG IV), each superseding the previous system. Thirteen researchers have been listed as authors to the three papers, and a further 43 as contributors (see Members of

#443556